The subject invention relates to a lithographic dampening solution which contains a micro-emulsion forming component in combination with a dampening solution concentrate. More specifically, a microemulsion is formed when the formulas disclosed herein are combined with a diluted commercial dampening solution concentrate. Further, the formulation does not include isopropyl alcohol or equivalent replacements therefor which are toxic or flammable and, therefore, hazardous in use.
The lithographic offset printing process involves the use of water-based solutions, known as dampening solutions, to wet the non-image areas of the printing plate and thereby prevent hydrophobic inks from depositing in those non-image areas. This is referred to as dampening. The mechanical part of the printing press that meters the fountain or dampening solution to the printing plate is referred to as the dampening system.
Dampening systems have undergone a considerable evolution in the past 40 years. One long standing characteristic is that many dampening systems function better when isopropyl alcohol is added to the dampening solution at levels of 3% to 25%.
The functions of isopropyl alcohol have been investigated extensively. When mixed into press-ready dampening solutions, isopropyl alcohol is a poor solvent for inks used in lithography. This is important to the rheology of printing inks. Proper ink rheology is critical to achieving a quality printed sheet at acceptable production rates. Many dampening systems are designed to mill a quantity of dampening solution into the ink during the lithographic printing process. Other dampening systems result in the incidental milling of dampening solution into ink. The milling of the ink and the dampening solution forms a water-in-oil emulsion. The poor ink solvency of isopropyl alcohol helps prevent excessive change in the rheological characteristics of inks that contain emulsified dampening solution. A further function of isopropyl alcohol is control of both the amount and the particle size of dampening solution which is emulsified into the printing ink. This characteristic has been difficult to achieve in conventional substitutes for isopropyl alcohol.
Other desirable properties of isopropyl alcohol include: (1) controlled increase of dampening solution viscosity allowing cohesive and uniform wet films to be pulled through the rollers of the dampening system; (2) controlled decrease in dynamic surface tension due to isopropyl alcohol acting as a bulk surface tension modifier; (3) reduction of the water settings on the press, which in turn enhances ink drying time; and, (4) universal application on the numerous different designs of dampening systems, used in the industry.
Isopropyl alcohol, however, presents a serious environmental problem in that it evaporates readily and quickly fills the atmosphere of printing shops. Isopropyl alcohol is a volatile organic compound at 6.7 pounds V.O.C. per gallon. Its use in printing systems is at fairly high levels, from 3% to 25% of the dampening solution, usually from 15% to 20% thereof. Isopropyl alcohol also presents problems due to its flammable nature. Federal legislation on air pollution has focused on reducing or eliminating emissions of isopropyl alcohol, as it is considered a volatile organic compound.
A number of replacements for isopropyl alcohol, as it is used in lithographic offset printing, have been suggested. In U.S. Pat. No. 4,560,410 a mixture of polyol and a partially water soluble glycol ether and a polyol and a completely water soluble glycol ether is described. A feature of this patent is the use of ethylene glycol, ethylene glycol ethers and 2-ethyl-l,3-hexanediol, all of which have some level of toxicity, and are affected by current legislation.
U.S. Pat. No. 5,006,168 describes the use of a water soluble cellulose ether as an alcohol substitute. This patent admits the need for isopropyl alcohol in some applications and therefore does not provide all the functional benefits of isopropyl alcohol modified dampening solutions.
A wide variety of nonionic compounds, mostly solvents, are listed in U.S. Pat. No. 4,278,467 as substitutive additives for isopropyl alcohol, 2-butoxyethanol being one of those identified therein. In fact, 2-butoxyethanol is one of the most widely used and effective replacements for isopropyl alcohol. This is attested to by years of use in the lithographic printing industry. 2-butoxyethanol is fairly effective and is used at much lower concentrations than isopropyl alcohol.
However, 2-butoxyethanol, not unlike isopropyl alcohol, has a drawback in that it has been shown to be toxic (ACGIH, TLV, 25 ppm [Skin]) and is readily absorbed through the skin in toxic amounts. The threshold limit value of 25 ppm for skin is fairly low and dampening solutions with 2-butoxyethanol typically contain a high level of 0.5% to 5% for effectiveness. Recent Federal legislation (1990 Clean Air Act Amendments) has identified 2-butoxyethanol and all ethylene glycol ethers as hazardous air pollutants with the goal being elimination of these solvents in coming years. Acceptable use levels or concentrations of most alcohol substitutes, especially 2-butoxyethanol, is limited because of resultant drastic changes in ink rheology, i.e. relatively low levels are used compared to isopropyl alcohol. For instance, 2-butoxyethanol has a limit of 0.5% to 5% of the dampening solution, as compared to isopropyl alcohol which is used at 3% to 25% and most often at 15% to 20% of the dampening solution.
The development of a true alternative to the use of isopropyl alcohol has been an elusive goal. All alternatives developed to this date have been deficient in achieving all of the desired characteristics of isopropyl alcohol.
It has remained for the invention described herein to resolve the technical problems associated with achieving performance equivalence to the use of isopropyl alcohol in lithographic printing without the attendant disadvantages of isopropyl alcohol use.